In the IP multimedia subsystem (IMS) type network, subscribers may have multiple terminals for making use of such network. In particular, these may include session initiation protocol (SIP) based terminals and global system for mobile communication (GSM) based terminals, or terminals that include both SIP signaling capability and GSM signaling capability and that may receive services from the GSM network and from the IMS network at the same time.
In the IP multimedia subsystem type networks, various solutions exist for providing extended services even to users in a GSM based network (or another circuit switched type telecommunications network). An example of such a solution is the BCS Mobility solution provided by Ericsson.
When a call is established by a subscriber using such extended services with his or her GSM terminal, there will be several charging records generated in the telecommunications system. The circuit switched part of the telecommunications network system operates based on call detail records that are generated by the mobile services switching centre (MSC) that serves the calling or called terminal. In the packet switched part of the telecommunications network system, such as in the IP multimedia subsystem (IMS) network, a session initiation protocol type application server which is responsible for handling the call between the parties engaged in the call, generates IMS charging records to be used for charging the services provided to the user. Charging of these calls will be done in the IMS network, based on the charging records generated by the SIP application server (SIP-AS).
In order to enable correct charging of the call in the IMS network, the charging record(s) from the IMS network generated by the SIP-AS need(s) to be correlated with the call detail records from the circuit switched part of the telecommunication network system. This is performed by a post processing system in the IMS network, which determines based on the charging record generated by the SIP-AS whether all data is available for charging the call, or correlation is required to correlate the charging record with one or more call detail records (CDR's) from the circuit switched part of the telecommunications network system.
The charging method of the prior art, as described for example above, contains a cumbersome and difficult step of correlating call detail data (being call related data from e.g. call detail records) from the circuit switched part of a telecommunications network system with charging records generated by the IMS network.